This invention relates generally to electronic power control systems for electrical loads which may be subject to a plurality of different supply voltages or to substantial swings relative to a nominal supply voltage.
In different geographic areas within the U.S. as well as among various countries throughout the world, the nominal supply voltages can differ significantly. Typical nominal RMS supply voltages are 208, 220, 240 volts. In addition, voltages can vary from the nominal supply value. In resistive heating elements such as may be employed in cooking appliances, relatively large output power changes can occur with relatively small changes in input voltages since output power varies with the square of the voltage. Similar changes can occur with non-resistive loads such as electric motors for washing machines, or inverter circuits for induction cooktops.
Rather than design a different control system for each different nominal supply voltage it would be desirable to provide a single cost effective control system for an appliance, for example, which would allow the appliance to be used with any of the various power supplies. To be attractive for such applications the control system should either automatically adapt to the applied voltage, or at least be readily and simply pre-settable to various supply voltages in the factory or during installation.
In addition, it would be desirable to provide a control system for an appliance which automatically compensates for temporary over-voltage conditions without any apparent difference in performance thereby preventing damage to the appliance, avoiding a potential safety hazard, all without interrupting use and enjoyment of the appliance.
It is therefore an object of the present invention to provide a control system for an electrical load such as in an appliance which automatically adapts to a variety of supply voltages and compensates for significant swings in a given nominal voltage supply.
It is another object of the present invention to provide a control system for an electrical load such as in an appliance which can be simply preset to a variety of different supply voltages either in the factory or in the home during installation.
It is yet another object of the present invention to provide a control system for an electrical load such as an appliance which automatically compensates for over-voltage condition without interrupting or otherwise adversely affecting operation of the load.